In an era of globally competitive and technology-driven societies, we are seeing a growing interest in developing a better understanding of the types of skills adults need to succeed both in the workplace and in everyday life. One large-scale comparative survey designed to inform that understanding is the OECD's Program for the International Assessment of Adult Competencies (PIAAC), a survey of adults ages 16-65 conducted in over 30 countries. PIAAC was designed for, and with, participating countries and represents a wide range of knowledge and skills that are required across a variety of adult contexts. The PIAAC data make it clear that adults with lower-level literacy and numeracy skills experience less favorable social, educational and labor market outcomes when compared with their more highly skilled cohorts. While some of those adults possess key foundational reading and numeracy skills, they would benefit from enhancing their skills so that they can more readily navigate, critically analyze, and problem solve in today's data-intensive, complex digital environments. This report describes a project in which two groups of experts -- one in the domain of literacy and the other in numeracy -- conducted analyses of the PIAAC data with the goal of defining the knowledge and skills associated with various levels of proficiency in those domains. The key purpose of this work is to form a foundation for the development of strategic interventions to improve adult literacy and numeracy skills. The argument made herein is that the insights gained from these expert analyses into the skills needed to transition to higher levels of literacy and numeracy can be leveraged to create a coherent learning and assessment system that could significantly enhance the literacy and numeracy skills of various adult populations.